Oncogenic transformation by Rous sarcoma virus is mediated by a single virus-encoded gene product, pp60src. Crucial to an understanding of the events involved in RSV-induced transformation is the identification of cellular proteins which interact with pp60src either as substrates of the pp60src-associated phosphotransferase activity or as regulatory proteins which ultimately affect the function of pp60src. We propose to investigate the interaction of this protein with two cellular proteins of Mr 90,000 (pp90) and 50,000 (pp50) which associate in a complex with pp60src in RSV-transformed cells. Because of the transient nature of this association of pp90 and pp50 with newly-synthesized molecules pf pp60scr before their association with the plasma membrane, we postulate that this complex may be involved in an event involving the processing of pp60src in the cytoplasm. Possible functional roles of this complex could involve the transport of pp60src from polyomes to the plasma membrane or regulation of the functional activity of pp60SPC. We plan to investigate both structural and functional aspects of this interaction in order to elucidate the role of this complex in pp60src-mediated oncogenesis. The structural studies are designed to determine the protein linkages within the pp50:pp60src: pp90 complex and to identify the sites on pp60src which are involved in this interaction. Since the domain of pp60src which is involved in membrane association and the domain containing phosphotransferase activity have been identified, this information should provide important functional information. Other studies are designed to further investigate the specificity of the interaction between pp90, pp50 and pp60src, the behavior of mutant viruses which have altered binding to pp90 and pp50, and the association of pp90 with normal cell pp60c-src and other cellular proteins. These studies should yield important information on one aspect of pp60src's interaction with the host cell. If pp90 and pp50 are found to associate with normal cellular proteins, these studies may elucidate a novel mechanism of cellular regulation which has not yet been identified.